US6680574B1 - Gas discharge lamp comprising an oxide emitter electrode - Google Patents

Gas discharge lamp comprising an oxide emitter electrode Download PDF

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Publication number
US6680574B1
US6680574B1 US09/718,252 US71825200A US6680574B1 US 6680574 B1 US6680574 B1 US 6680574B1 US 71825200 A US71825200 A US 71825200A US 6680574 B1 US6680574 B1 US 6680574B1
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United States
Prior art keywords
oxide
earth metal
coating
alkaline earth
rare earth
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Expired - Fee Related, expires
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US09/718,252
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English (en)
Inventor
Georg Gaertner
Wim Van Den Hoek
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Koninklijke Philips NV
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Koninklijke Philips Electronics NV
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Assigned to U.S. PHILIPS CORPORATION reassignment U.S. PHILIPS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GAERTNER, GEORG, VAN DEN HOEK, WIM
Assigned to KONINKLIJKE PHILIPS ELECTRONICS N.V reassignment KONINKLIJKE PHILIPS ELECTRONICS N.V ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: U.S. PHILIPS CORPORATION
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/067—Main electrodes for low-pressure discharge lamps
    • H01J61/0675—Main electrodes for low-pressure discharge lamps characterised by the material of the electrode

Definitions

  • the invention relates to a gas discharge lamp, in particular a low-pressure gas discharge lamp, which comprises an electrode including a carrier and a coating of an electron-emitting material, which material comprises an alkaline earth metal oxide, which is selected from the group formed by calcium oxide, strontium oxide and barium oxide, and an oxide of a rare earth metal.
  • the generation of light in a gas discharge lamp is based on the ionization, and the resulting electric discharge, of the atoms of the filling gas in the lamp when an electric current flows through the lamp.
  • the electrodes of the lamp emit electrons, which are so strongly accelerated by the electric field between the electrodes that, upon colliding with the gas atoms, they are capable of exciting and ionizing the latter.
  • the gas atoms return to the ground state, and also in the case of the recombination of electrons and ions, a more or less substantial part of the potential energy is converted to radiation.
  • the number of electrons that can be emitted by the electrodes depends upon the work function of the electrodes for electrons.
  • Tungsten which is customarily used as the electrode metal, has a comparatively high work function.
  • the electrode metal is customarily coated with a material which serves to improve the electron-emitting properties of the electrode metal. It is typical of the electron-emitting coating materials of electrodes in gas discharge lamps that they contain an alkaline earth metal, either in the form of the alkaline earth metal oxide or in the form of an alkaline earth metal-containing starting compound (precursor) for the alkaline earth metal oxide.
  • conventional low-pressure gas discharge lamps are generally provided with electrodes which are composed of tungsten wires with an electron-emitting coating containing oxides of the alkaline earth metals calcium, strontium and barium.
  • a tungsten wire is coated, for example, with the carbonates of the alkaline earth metals in a binder preparation.
  • the carbonates are converted into the oxides at temperatures of approximately 1000° C.
  • the electrode already supplies a noticeable emission current which, however, is not stable yet.
  • an activation process is carried out. Due to this activation process, the originally non-conducting ion lattice of the alkaline earth oxides is converted to an electronic semiconductor. In this process, donor-type imperfections are incorporated into the crystal lattice of the oxides. These lattice imperfections essentially consist of elementary alkaline earth metal, for example calcium, strontium or barium.
  • the electron emission of such electrodes is based on this mechanism of lattice imperfections.
  • the activation process serves to provide a sufficient quantity of excess, elementary alkaline earth metal, enabling the oxides in the electron-emitting coating to supply as much emission current as possible at a prescribed heating capacity.
  • the elementary alkaline earth metal is initially dispensed continuously by a reduction of the alkaline earth oxide at the tungsten wire during operation of the lamp. However, this dispensation stops when the tungsten wire is passivated, in the course of time, by a highly resistive interface of tungsten oxide, alkaline earth silicate or alkaline earth tungstate.
  • DE 1 021 482 discloses a method of manufacturing an oxide cathode for low-pressure discharge lamps, the activating substance of which is composed of a mixture of barium oxide, strontium oxide and calcium oxide, which are formed during the activation of the cathode by thermal decomposition of the alkaline earth carbonates used as the starting material, an inactive additive composed of at least one oxide of the elements: titanium, germanium, aluminum and other elements of group III of the periodic system, particularly the rare earth elements, being added to the alkaline earth-carbonate mixture in such a quantity that the overall quantity of the added oxides in the completely activated cathode does not exceed the smallest quantity of alkaline earth oxide used, and the cathode is activated by heating to a temperature below 1,000° C., preferably 800° C. to 900° C.
  • This method has the advantage that the carbonates are rapidly decomposed at low temperatures and the lamp does not contain carbonic acid.
  • a gas discharge lamp comprising an electrode including a carrier of an electrode metal, selected from the group formed by tungsten and tungsten-containing alloys, and a first coating of a first electron-emitting material, which material comprises an alkaline earth metal oxide, selected from the group formed by calcium oxide, strontium oxide and barium oxide, and a rare earth metal oxide selected from the group formed by scandium oxide, yttrium oxide and europium oxide in a quantity that ranges from 0.1 to 10 wt. % by weight.
  • the passivation of the electrode metal is reduced, so that alkaline earth metal is released from the oxide over a longer period of time and the work function of the electrode remains low. This results in a shorter ignition stage of the lamp.
  • the addition of a rare earth metal oxide in a quantity “A” that ranges from 0.1 to 10 wt. % by weight, brings about a reduction of the evaporation of elementary alkaline earth metal and hence leads to a longer service life.
  • the electrode has a high initial emission and contains sufficient elementary alkaline earth metal throughout the service life of the lamp. The availability of sufficient elementary alkaline earth metal also leads to a high resistance to poisoning by oxygen.
  • a second coating of a second electron-emitting material is arranged between the carrier and the first coating, said second electron-emitting material comprising an alkaline earth metal oxide, selected from the group formed by calcium oxide, strontium oxide and barium oxide, and a rare earth metal oxide, selected from the group formed by scandium oxide, yttrium oxide and europium oxide, in a quantity “B” that ranges from 2.0 to 20% by weight.
  • a third coating between the carrier and the first coating which third coating is composed of a noble metal selected from the group formed by rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum.
  • a gas discharge lamp has a reduced ignition stage, and the electrode accommodated in such a lamp has an improved conductivity.
  • the first electron-emitting material comprises zirconium oxide. It may also be preferred that the second electron-emitting material comprises zirconium oxide.
  • the first electron-emitting material comprises a metal powder preparation of a metal selected from the group formed by aluminum, silicon, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten and the alloys thereof, which metal powder preparation is provided with a powder coating of a noble metal selected from the group formed by rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium and platinum.
  • FIG. 1 diagrammatically shows the generation of light in a fluorescent lamp.
  • Gas discharge lamps can be divided into low-pressure lamps and high-pressure lamps. They differ in the way in which they stabilize the discharge.
  • FIG. 1 shows, by way of example, a low-pressure discharge lamp with a mercury filling, i.e. a fluorescent lamp.
  • a gas discharge lamp is composed of a rod, ring or U-shaped glass tube 1 .
  • electrodes 2 At the ends of the tube there are electrodes 2 .
  • dual-pin caps 3 For the connection use is made of dual-pin caps 3 .
  • the inner surface of the glass tube is provided with a phosphor layer 4 , the chemical composition of which determines the spectrum of the light or its chrominance.
  • the glass tube contains a small quantity of mercury or mercury vapor which, when rendered luminescent under operating conditions, emits the Hg resonant line at a wavelength of 253.7 nm in the ultraviolet range.
  • the UV radiation emitted excites the phosphors in the phosphor layer, thereby causing them to emit light in the visible range 5 .
  • the lamp also comprises means for igniting and for operating, for example a fluorescent lamp ballast and a starter.
  • a gas discharge lamp in accordance with the invention comprises an electron-emitting electrode, which includes a carrier of an electrode metal and a first coating containing an electron-emitting material.
  • the carrier of an electrode metal is customarily made of tungsten or a tungsten alloy, possibly with a molybdenum core.
  • the carrier may be in the form of a wire, a coil, a spiral, an undulated wire, a tube, a ring, a plate or a tape.
  • the carrier is customarily heated directly by the current flow.
  • the carrier of an electrode metal may be additionally provided with a coating of a noble metal selected from the group formed by rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum.
  • a noble metal selected from the group formed by rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum.
  • the coating is a 0.1 to 2 ⁇ m thick iridium or rhenium layer.
  • the raw material for the electron-emitting substance of a first coating is applied to this carrier.
  • the carbonates of the alkaline earth metals selected from the group formed by calcium, strontium and barium are mixed with a quantity a of a rare earth metal oxide that ranges from 0.1 to 10% by weight, said rare earth metal oxide being selected from the group formed by scandium oxide, yttrium oxide and europium oxide.
  • the weight ratio of calcium carbonate:strontium carbonate:barium carbonate typically is 1:1.25:6 or 1:12:22 or 1:1.5:2.5 or 1:4:6.
  • the mixture of alkaline earth oxides and rare earth metal oxide can be prepared by coprecipitation, in that a water-soluble compound of the rare earth metals is added to a solution of the alkaline earth nitrates, whereafter the alkaline earth carbonates and the rare earth metal oxides are precipitated by the addition of sodium carbonate.
  • the electron-emitting material may comprise further components, for example zirconium oxide.
  • a metal powder of the metals of the group formed by aluminum, silicon, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten, and their alloys with a metal of the group formed by rhenium, rhodium, palladium, iridium and platinum having a powder coating of iridium, rhenium, rhodium, platinum, palladium, nickel and cobalt can be added to the electron-emitting material.
  • a metal powder having an average grain size of 2 to 3 ⁇ m with a 0.1 to 0.2 ⁇ m thick powder coating is used.
  • CVD methods such as fluid-bed CVD. This coated metal powder is added to the raw material.
  • the raw material may additionally be mixed with a binder. Subsequently, the raw material is applied to the carrier by means of brushing, dip coating, cataphoretic deposition or spraying.
  • a second electrode coating of a second electron-emitting material may be arranged between the carrier and the first electrode coating, said second electron-emitting material comprising an alkaline earth metal oxide, selected from the group formed by calcium oxide, strontium oxide and barium oxide, and a rare earth metal oxide, selected from the group formed by scandium oxide, yttrium oxide and europium oxide, in a quantity b that ranges from 2.0 to 20% by weight.
  • the second electron-emitting material may additionally contain zirconium oxide or a metal powder of the metals selected from the group formed by aluminum, silicon, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten and their alloys with a metal selected from the group formed by rhenium, palladium, rhodium, iridium and platinum, which is provided with a powder coating of iridium, rhenium, rhodium, platinum, palladium, nickel and cobalt.
  • the coated electrodes are sealed in the end portions of the lamp.
  • the electrodes are activated during evacuating and filling the lamp.
  • the electrode wire is heated to a temperature in the range from 1000° C. to 1200° C. by direct passage of current.
  • the alkaline earth carbonates are converted, while releasing CO and CO 2 , to alkaline earth oxides, and then form a porous sintered body.
  • a second activation process is carried out, which serves to supply excess elementary barium intercalated into the oxides. Said excess barium is formed by the reduction of barium oxide.
  • barium oxide is reduced by the released CO or by the carrier metal.
  • a current activation process is carried out which enables the required free barium to be formed by electrolytic processes at high temperatures.
  • the oxides evaporate slowly as a result of the ion bombardment in the focal point.
  • a triple-coiled tungsten wire is coated with iridium in a layer thickness of 1.0 ⁇ m.
  • 3 wt. % scandium-oxide powder having an average grain size of 2 ⁇ m and 3 wt. % zirconium metal are added to a triple carbonate mixture composed of BaCO 3 :SrCO 3 :CaCO 3 in a ratio of 1.6:1.25:1, whereafter they are mixed and processed with butyl acetate and cellulose nitrate.
  • This suspension is brushed onto the coated tungsten wire, whereafter said wire is introduced into a lamp bulb and heated to 1000° C.
  • the carbonates of the alkaline earth metals convert to their oxides and the zirconium metal converts to zirconium oxide.
  • an activation process may be carried out.
  • Such a lamp has a long service life, a short ignition stage, a low work function of 1.42 eV and a conductivity which is improved by a factor of 2.
  • a quantity of 5 wt. % scandium oxide is admixed with a triple carbonate composed of BaCO 3 :SrCO 3 :CaCO 3 in a ratio of 22:12:1, whereafter the mixture is suspended with butyl acetate and cellulose nitrate and brushed onto a double-coiled tungsten wire, whereafter said wire is introduced into a lamp bulb and heated to 1000° C. Following this bum-in process, an activation process may be carried out.
  • a quantity of 3 wt. % yttrium oxide powder having an average grain diameter of 2.5 ⁇ m is admixed with a triple carbonate composed of BaCO 3 :SrCO 3 :CaCO 3 in a ratio of 2.5:1.5:1, whereafter the mixture is suspended with butyl acetate and cellulose nitrate and brushed onto a double-coiled tungsten wire, whereafter said wire is introduced into a lamp bulb and heated to 1000° C. Following this burn-in process, an activation process may be carried out.
  • a lamp is characterized by a longer service life and a higher resistance to poisoning.
  • An electron-emitting substance is prepared from a triple carbonate composed of BaCO 3 :SrCO 3 :CaCO 3 in a ratio of 6:4:1, which is admixed with 0.02 wt. % europium oxide powder by coprecipitation, and from a further 3 wt. % europium oxide having an average grain diameter of 4.0 ⁇ m.
  • the mixture is suspended with butyl acetate and cellulose nitrate and brushed onto a triple-coiled tungsten wire, whereafter said wire is introduced into a lamp bulb and heated to 1000° C. Following this burn-in process, an activation process may be carried out.
  • Such a lamp is characterized by a longer service life, a higher resistance to poisoning and a robust manner of coping with a rapid succession of switching operations.

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  • Discharge Lamp (AREA)
US09/718,252 1999-11-29 2000-11-22 Gas discharge lamp comprising an oxide emitter electrode Expired - Fee Related US6680574B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19957420A DE19957420A1 (de) 1999-11-29 1999-11-29 Gasentladungslampe mit Oxidemitter-Elektrode
DE19957420 1999-11-29

Publications (1)

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US6680574B1 true US6680574B1 (en) 2004-01-20

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US (1) US6680574B1 (fr)
EP (1) EP1104933A3 (fr)
JP (1) JP2001189145A (fr)
CN (1) CN1298197A (fr)
DE (1) DE19957420A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070064372A1 (en) * 2005-09-14 2007-03-22 Littelfuse, Inc. Gas-filled surge arrester, activating compound, ignition stripes and method therefore
US20070120456A1 (en) * 2005-11-28 2007-05-31 General Electric Company Barium-free electrode materials for electric lamps and methods of manufacture thereof
US20070120482A1 (en) * 2005-11-30 2007-05-31 Michael Joseph D Electrode materials for electric lamps and methods of manufacture thereof
US20070278929A1 (en) * 2004-04-20 2007-12-06 Fujian Gpb Enterprises Limited Hot Cathode Fluorescent Lamp Without Filament
US20080237541A1 (en) * 2007-03-30 2008-10-02 General Electric Company Thermo-optically functional compositions, systems and methods of making
WO2008139368A1 (fr) * 2007-05-10 2008-11-20 Philips Intellectual Property & Standards Gmbh Lampe à décharge de gaz à remplissage de gaz comprenant du chalcogène
US20090302765A1 (en) * 2008-06-06 2009-12-10 Istvan Deme Emissive electrode materials for electric lamps and methods of making

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* Cited by examiner, † Cited by third party
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DE10232239A1 (de) * 2002-07-17 2004-02-05 Philips Intellectual Property & Standards Gmbh Niederdruckgasentladungslampe mit Elektrode
DE10242241A1 (de) * 2002-09-12 2004-03-25 Philips Intellectual Property & Standards Gmbh Niederdruckgasentladungslampe mit Ba TiO3-ähnlichen Elektronen-Ermittersubstanzen
DE102009021235B4 (de) * 2009-05-14 2018-07-26 Osram Gmbh Entladungslampe mit beschichteter Elektrode
US20120187871A1 (en) * 2009-09-17 2012-07-26 Osram Ag Low-pressure discharge lamp
CN102142342B (zh) * 2011-03-03 2012-07-25 广州慧沣电子科技有限公司 一种钡钨电极的制备方法
CN103560061A (zh) * 2013-07-26 2014-02-05 江西耀宇光电科技有限公司 一种灯丝材料及其制备工艺

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1021482B (de) 1952-04-24 1957-12-27 Egyesuelt Izzolampa Verfahren zur Herstellung einer Oxydkathode fuer Niederdruck-Entladungslampen und andere gasgefuellte elektrische Entladungsroehren
US3582702A (en) * 1968-04-04 1971-06-01 Philips Corp Thermionic electron-emissive electrode with a gas-binding material
US4303848A (en) * 1979-08-29 1981-12-01 Toshiba Corporation Discharge lamp and method of making same
US5585694A (en) * 1990-12-04 1996-12-17 North American Philips Corporation Low pressure discharge lamp having sintered "cold cathode" discharge electrodes
US5847498A (en) * 1994-12-23 1998-12-08 Philips Electronics North America Corporation Multiple layer composite electrodes for discharge lamps
US6054802A (en) * 1996-06-20 2000-04-25 Mitsubishi Denki Kabushiki Kaisha Cathode for electronic tube

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR694941A (fr) * 1929-07-02 1930-12-09 Tubes à décharge, en particulier tubes luminescents et irradiants
US5962977A (en) * 1996-12-20 1999-10-05 Ushiodenki Kabushiki Kaisha Low pressure discharge lamp having electrodes with a lithium-containing electrode emission material

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1021482B (de) 1952-04-24 1957-12-27 Egyesuelt Izzolampa Verfahren zur Herstellung einer Oxydkathode fuer Niederdruck-Entladungslampen und andere gasgefuellte elektrische Entladungsroehren
US3582702A (en) * 1968-04-04 1971-06-01 Philips Corp Thermionic electron-emissive electrode with a gas-binding material
US4303848A (en) * 1979-08-29 1981-12-01 Toshiba Corporation Discharge lamp and method of making same
US5585694A (en) * 1990-12-04 1996-12-17 North American Philips Corporation Low pressure discharge lamp having sintered "cold cathode" discharge electrodes
US5847498A (en) * 1994-12-23 1998-12-08 Philips Electronics North America Corporation Multiple layer composite electrodes for discharge lamps
US6054802A (en) * 1996-06-20 2000-04-25 Mitsubishi Denki Kabushiki Kaisha Cathode for electronic tube

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070278929A1 (en) * 2004-04-20 2007-12-06 Fujian Gpb Enterprises Limited Hot Cathode Fluorescent Lamp Without Filament
US20070064372A1 (en) * 2005-09-14 2007-03-22 Littelfuse, Inc. Gas-filled surge arrester, activating compound, ignition stripes and method therefore
US7643265B2 (en) 2005-09-14 2010-01-05 Littelfuse, Inc. Gas-filled surge arrester, activating compound, ignition stripes and method therefore
US20070120456A1 (en) * 2005-11-28 2007-05-31 General Electric Company Barium-free electrode materials for electric lamps and methods of manufacture thereof
US7633216B2 (en) * 2005-11-28 2009-12-15 General Electric Company Barium-free electrode materials for electric lamps and methods of manufacture thereof
US20070120482A1 (en) * 2005-11-30 2007-05-31 Michael Joseph D Electrode materials for electric lamps and methods of manufacture thereof
US7633226B2 (en) * 2005-11-30 2009-12-15 General Electric Company Electrode materials for electric lamps and methods of manufacture thereof
US20080237541A1 (en) * 2007-03-30 2008-10-02 General Electric Company Thermo-optically functional compositions, systems and methods of making
WO2008139368A1 (fr) * 2007-05-10 2008-11-20 Philips Intellectual Property & Standards Gmbh Lampe à décharge de gaz à remplissage de gaz comprenant du chalcogène
US20090302765A1 (en) * 2008-06-06 2009-12-10 Istvan Deme Emissive electrode materials for electric lamps and methods of making
US7786661B2 (en) 2008-06-06 2010-08-31 General Electric Company Emissive electrode materials for electric lamps and methods of making

Also Published As

Publication number Publication date
CN1298197A (zh) 2001-06-06
JP2001189145A (ja) 2001-07-10
EP1104933A2 (fr) 2001-06-06
DE19957420A1 (de) 2001-05-31
EP1104933A3 (fr) 2004-08-25

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